Electrophotographic processes are used to form images on substrates. Common electrophotographic processes are photocopying and laser printing. In these processes, a latent charge image is created. A toner is applied to the image, and the image is developed and is transferred to a substrate. The substrate can be anything that accepts the image, such as paper, textiles, plastic, or foils. The image is permanently affixed to the substrate by one or more of the following methods, heat, pressure, irradiation, or exposure to solvents.
The toner generally contains a binder, a colorant, an electrostatically chargeable component, and other auxiliary compounds. Toners need to be capable of acquiring and maintaining an electrical charge to allow the toner particles to be electrostatically bound to the image area until the toner can be fixed to the substrate.
Generally, the electrical charge is imparted to the toner by means of tribo-electric charging. Tribo-electric charging is static electric charge that is built up by the motion of the particles being stirred or otherwise flowing over one another. The tribo-electric charge is normally introduced in the toner by the addition of a charge control agent, which is a material capable of building and holding a charge. Charge control agents can be azo-metal dye complexes, quaternary amine salts, polymeric salts, or triphenylmethanes. The charge control agents may me colored or colorless depending on their structure.
Solvent Blue 23 is may be used as a pigment in printing inks. Solvent Blue 23 can be sulfonated to form Pigment Blue 61, which is normally used as a pigment in printing inks. Pigment Blue 61 is a mixture of sulfonation products. In the printing ink field, Solvent Blue 23 is generally sulfonated from 50 to 100% by mole fraction of the Solvent Blue 23 to form Pigment Blue 61. For some printing ink applications, the degree of sulfonation can be as low as 30%. Sulfonation can be accomplished by the methods disclosed in U.S. Pat. No. 4,944,806 to Sharangpani et al., which is incorporated herein by reference.
Attempts have been made to use Pigment Blue 61 as a charge control agent (see U.S. Pat. No. 5,061,585 to Macholdt et al. at column 3, lines 31-52 and column 5, line 58 to column 6, line 2). Using Pigment Blue 61 at standard levels of sulfonation did not provide good results. This Pigment Blue 61 typically has a sulfonation level between 45 to 90%, and is usually 55 to 75%.
It would be desirable to have a charge control agent that provides a desired positive charge level.